Green tea, the most commonly consumed beverage in the world after water, offers some important health benefits. The compounds believed to be responsible for these benefits are polyphenols and in particular catechins.
The major green tea polyphenols (flavan-3-ol) are catechins, i.e. (+)-catechin (C) and its stereoisomer and four derivatives, namely (−)-epicatechin (EC), (−)-epigallocatechin (EGC), (−)-epigallocatechin-3-gallate (EGCg), (−)-epicatechin-3-gallate (ECg).
Although amounts of catechins vary depending on the factors influencing plant metabolism such as light, rain fall, temperature, nutrient availability, leaf age, and genetic make-up, they usually constitutes 20-30% of the dry matter of fresh green tea leaves. Catechins represent approximately 80% of the total polyphenol content of green tea. As they are rarely destroyed during manufacturing of green tea, catechins are a major part of commercial green tea extracts.
Green tea catechins display several health benefits that are often associated to their antioxidant activities including scavenging of reactive oxygen and nitrogen species, free metal chelation, inhibition of transcriptional factors and inhibition of oxidative enzymes such as lipoxygenase and cycloxygenase.
The health effects of polyphenols depend on the amount consumed and on their bioavailability. However their bioavailability is poor, which seems to be linked to a particular instability of these compounds under physiological conditions.
One possible strategy to increase the stability of green tea catechins under adverse conditions is to protect them by antioxidants thus preventing the chemical changes caused by exposure to oxygen. For example, Rode et al. (2002) have shown that the incorporation of a hydrosoluble antioxidant (vitamin C) stabilized green tea catechins in emulsions but they did not see any effect when they used lipophilic antioxidants such as butylated hydroxytoluene or propyl gallate. Indeed, all four catechin species and, in particular, EgC and EgCg were found to be stabilized in the presence of ascorbic acid and this protection is dose-dependent. Even though this protective effect of ascorbic acid has long been known, its effect on bioavailability has never been confirmed. In fact in G. Williamson et al., Int. J. Vitam. Nutri Res. 77 (3) 2007, 224-235, it has been recently showed that the addition of antioxidant (vitamins and carotenoids) had no effect on bioavailability of polyphenols such as catechins.
It is thus an object of the present invention to address the above problems by providing a formulation that contains catechins with improved stability and increased bioavailability. It is also an object of the present invention to provide a green tea formulation that has an increased bioavailability which can be used for applications in food or pet food products, nutritional or food supplements, cosmetic or pharmaceutical preparations.